Are Onions Good for Compost? The Complete Guide

Onions are a staple in many kitchens. Their pungent, aromatic flavor adds depth and savoriness to soups, stews, casseroles, and more But when it comes time to compost your onion scraps, should onions go in the compost bin?

There’s a lot of conflicting information out there about composting onions. Some sources claim onions are harmful to compost piles. Others say they’re perfectly fine to add. So what’s the truth?

In my experience, onions can absolutely be composted. However, there are a few best practices to follow when adding onions to your compost to avoid potential issues. Here’s what you need to know.

The Benefits of Composting Onions

First, let’s look at why composting onions can be a good thing.

• Nitrogen – Onions contain moderate levels of nitrogen an essential nutrient for healthy compost, Nitrogen provides energy for the microbes and bacteria that break down organic matter in the compost pile

• Sulfur – Onions contain sulfur compounds, which help reduce pH levels in compost. Lower pH levels assist with decomposition.

• Moisture – The high moisture content in onions helps provide the dampness compost piles need to encourage decomposition.

• Organic material – Like any vegetable scraps, onions add valuable organic matter to the compost mix.

So in many ways, onions offer substantial upside as a compost ingredient. Next, let’s look at how to compost onions successfully.

Best Practices for Composting Onions

While onions can certainly go in the compost bin there are some best practices to follow:

• Chop Onions Before Composting – Whole, intact onions are not ideal for compost piles. Whole onions may take longer to break down. And if left long enough, they could sprout and grow inside the compost bin! Chopping onions into smaller pieces speeds up decomposition. Aim to chop onions into 1/2 inch pieces or smaller before adding to compost.

• Bury Onion Scraps in the Center of the Pile – Onion scraps buried near the center of the compost pile will break down faster. This placement also helps contain onion odors.

• Balance Onions with Carbon-Rich Material – If adding a lot of onion waste, balance it out by mixing in carbon-rich “browns” like dried leaves, sawdust, or shredded newspaper. The carbon will balance the high nitrogen levels in onions.

• Don’t Put Rotten or Moldy Onions in Compost – While onion skins and trimmings are fine, avoid adding onions that are rotten or moldy. The microbes and fungi causing the rot are better off kept out of the compost pile.

• Avoid Cooked Onions – Raw onion scraps are ideal. Avoid cooked onions, as the oil and fat can slow decomposition and cause odors.

Following these tips will allow you to compost onions successfully!

What About Garlic and Other Alliums?

The same rules apply to other allium vegetable scraps like garlic, leeks, shallots, and scallions. Feel free to compost all alliums by chopping them first and burying in the center of the pile.

Just avoid adding any alliums that are diseased or rotten. And go easy on cooked alliums containing oils and fats.

Can Onions Go in Worm Composting Bins?

Worm composting, or vermicomposting, comes with a few extra considerations when composting onions.

Some experts advise keeping onions out of worm compost bins altogether. Onions may irritate worms’ skin and throw off the neutral pH balance worm bins require.

However, others have composted onions in moderation in worm bins without issue. If composting onions with worms, be sure to:

• Chop onions especially small, into 1/4 inch or tinier pieces.
• Bury onion scraps well below the top layers.
• Avoid adding onions in excess.
• Monitor closely and remove onions if they seem to bother worms.

So with some care, onions can potentially be vermicomposted. But they do carry some extra risks compared to traditional compost piles.

Are Onion Skins and Peels Compostable?

Absolutely! The papery outer skins from onion bulbs are completely compostable.

There is no need to remove the skins before adding onion scraps to compost. The skins provide valuable fiber.

Onion skins break down quickly and will not cause issues in compost piles or worm bins.

Are There Any Risks of Composting Onions?

Overall, onions are considered very safe to add to compost piles and provide substantial benefits. However, a few minor risks to be aware of:

• Strong odor – The sulfur compounds making onions aromatic can cause strong temporary odors, especially if onions are not buried within the pile.

• Acidity – Onions are moderately acidic. Excessive amounts could lower compost pH more than desired. But normal onion volumes are not a concern.

• Nitrogen imbalance – Too many onions and not enough carbon could cause excess nitrogen. But this is easily fixed by adding more “brown” material.

• Pests – Exposed onion scraps could attract pests before fully breaking down. But buried onion scraps are generally not a pest concern.

So while onions come with a few cautions, they do not pose any major risks or problems in compost. The benefits onions provide outweigh any potential downsides.

What About Onion Relatives Like Chives and Leeks?

Other vegetables in the allium family like chives, leeks, shallots, and green onions can all be composted similarly to regular bulb onions.

Follow the same tips of chopping the alliums, burying in the center of the pile, and balancing with carbon-rich materials. Avoid rotten or diseased alliums.

So feel free to compost all allium scraps! They provide valuable nutrients and organic matter for your compost.

Many home composters have questions about the suitability of composting onion waste. But onions can absolutely be composted effectively and beneficially.

Chop onions before adding to compost piles or bins. Bury onion scraps within the center of the pile. Balance onions with carbon-rich materials like leaves or straw. And avoid diseased onions or cooked onions with fat or oil.

Following these simple tips will allow you to take full advantage of onions’ nutrients and organic matter. Onions can rot and decompose just like any other vegetable waste in a well-managed compost bin or pile.

So feel confident adding onion scraps and skins into your compost! They provide nitrogen, sulfur, moisture, and fiber that all contribute to healthy, nutrient-rich compost for your garden.